Acetabular Fixation System and Method

ABSTRACT

Improved methods, devices, systems and models for facilitating supplemental fixation of implant components to surrounding anatomical features, including supplemental fixation of acetabular components to the acetabulum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from and is a continuation of U.S.patent application Ser. No. 14/210,437 filed on Mar. 14, 2014, entitled“ACETABULAR FIXATION SYSTEM AND METHOD” which in turn claims the benefitof U.S. Provisional Patent Application Ser. No. 61/784,171 entitled“Acetabular Fixation System and Method,” filed Mar. 14, 2013, thedisclosures of which are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

The invention relates to improved orthopedic implants, as well asrelated methods, designs, systems and models. More specifically,disclosed herein are improved methods, designs and/or systems for jointimplant components that facilitate supplemental fixation of anacetabular component to the acetabular bone.

BACKGROUND OF THE INVENTION

Acetabular components are typically implanted into the acetabular bonein a press fit manner and primarily rely on the ingrowth of bone ontothe porous outer surface of the acetabular component. Alternativefixation between the acetabular component and the acetabular bone ispossible with multiple different types of screw and peg options.Multiple different types of porous outer surfaces exist to improve thefixation of the acetabular component to the bone as well.

Most acetabular components typically have an opening at their apex(epicenter) of the hemisphere. This opening has a threaded screw hole sothat the acetabular component can accept the threads on an acetabularimpaction handle. This screw hole is typically located at the apexbecause the force generated from the mallet impacting the impactionhandle is desirably directed in line with the opening of the acetabularcomponent so the component does not change orientation of the opening ofthe acetabular component. The impaction force is desirably a truecompression force that does not create a rotation moment as theacetabular component enters the prepared hemisphere in the acetabularbone. For the same reason that it is beneficial for the impaction forceto be directed at the apex of the hemisphere, it is also beneficial forany alternative fixation devices to also direct their force in line withthe apex of the hemisphere.

This opening in the acetabular component is sometimes closed with a domescrew cap or cover at the end of the case to prevent the fluid frominside the acetabular component from entering the bone over the 20 to 30year life span of the implant. Joint fluid can carry polyethylene debristhat encourages osteolysis.

Most alternative fixation devices rely on a screw obtaining purchase inthe acetabular bone. These screw holes are located at differentlocations in the acetabular component. The screws are typically located30 to 40 degrees away from the apex of the acetabular component. Thescrew holes are located in this position because surgeons typically wantto advance screws into a substantial piece of acetabular bone and awayfrom neurovascular structures. The thickness of acetabular bone isgreatest in a superior direction, so most screws are positioned in asuperior direction. The thickness of the bone located in the directionof the apex of the hemisphere can sometimes limit the amount of boneavailable to be purchased by a screw. Therefore, screws are often notused in the dome screw hole, but are generally used 30 to 40 degreesaway from the apex where the bone is thicker. When the screw is somedistance away from the apex, there can be a compression stress betweenthe acetabular bone and acetabular component at the screw location, buta tensile stress on the opposite side of the acetabular component fromthe moment that is generated by obtaining fixation on just one side ofthe component. This tensile stress can lead to micro-motion of theacetabular component, failure of acetabular component in-growth andpossibly loosening of the acetabular component.

The joint reactive force in an acetabular component is typicallydirected in a mostly superior and slightly medial direction as thepatient's body weight pushes down and the prosthetic hip pushes up. Thissuperior directed force can cause a moment force of the acetabularcomponent that causes a compressive force superiorly and a tensile forcemedially. The superior directed screw is not ideally positioned toresist this moment force. A medially directed screw would be betterpositioned to resist this moment force, but the thickness of bonemedially prevents adequate screw purchase in most situations.

Alternative fixation between the acetabular component and the acetabularbone is increasingly important in acetabular revision surgery. When apatient has had an acetabular component implanted and then laterremoved, the acetabular bone is generally less receptive to anotheracetabular component. Obtaining adequate initial acetabular componentfixation is more difficult in a revision setting, and surgeons oftenhave to rely on these alternative fixation devices. Surgeons will oftenimplant multiple screws through the many screw holes in the acetabularcomponent into multiple locations of the acetabular bone.

Various surgical devices in the past have sought to obtain additionalfixation between the acetabular component and acetabular bone, but thesedevices have various limitations. See, for example, the devicesdisclosed in U.S. Pat. No. 2,765,787 filed on Aug. 2, 1954, U.S. Pat.No. 5,549,691 filed on Feb. 3, 1994, U.S. Patent Application Number20070142921 filed Dec. 21, 2005 and U.S. Patent Application Number20070142922, filed Dec. 21, 2005.

BRIEF SUMMARY OF THE INVENTION

Acetabular components can be attached to acetabular bone using amultitude of different devices, methods, systems and means. Variousembodiments disclosed herein include the deployment of an endobuttonthrough an existing hole in an acetabular component, through theacetabular bone, and to the inner table of the pelvic bone. Theendobutton could be rotated to grab the inner table of the pelvic bone.A suture could then contract and/or draw the endobutton to theacetabular component, desirably creating considerable compressionbetween the acetabular bone and acetabular component. The suture couldbe tightened in a variety of ways, including by using a mechanicaladvantage system like a gear mechanism, and the suture can bepermanently secured to the acetabular component, such as by using ametal dome screw that could thread into the dome screw threads at theapex of the acetabular component.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing and other objects, aspects, features, and advantages ofembodiments will become more apparent and may be better understood byreferring to the following description, taken in conjunction with theaccompanying drawings, in which:

FIGS. 1a and 1b depict perspective views of one embodiment of anacetabular insertion handle and an acetabular component;

FIG. 2 depicts a front plan view of one embodiment of an endobuttonsecurement device, showing the positioning sutures on either end of theendobutton and the central suture that could connect to the acetabularcomponent;

FIG. 3 depicts a cross-sectional view of an acetabular component, a domescrew, and an endobutton preloading inside the dome screw;

FIGS. 4a and 4b depict front plan views of exemplary positioning suturesthat can be attached to the endobutton;

FIG. 5 depicts a cross-sectional view of an endobutton that is deployedon one side of a bone (i.e., an acetabulum), a suture attached to theendobutton, a component (i.e., an acetabular component) implanted in abone (i.e., an acetabulum), and a dome screw;

FIGS. 6a and 6b depict cross-sectional views of an endobutton on oneside of a bone (acetabulum), a suture attached to the endobutton, acomponent (acetabular component) implanted in a bone (acetabulum), adome screw attached to the component, and an interference screw; and

FIGS. 7a and 7b depict cross-sectional views of an endobutton on oneside of a bone (acetabulum), a suture attached to the endobutton, acomponent (acetabular component) implanted in a bone (acetabulum), adome screw attached to the component, an interference screw, and aninterference screw engaging the suture and dome screw.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1a depicts a perspective view of an acetabular insertion handle 1,an acetabular component 2 and a threaded dome screw hole 3 at the apexof the acetabular component. FIG. 1b depicts a perspective view of anacetabular insertion handle 1 attached to an acetabular component 2. Theattachment can be via the threads in the dome screw hole.

In this embodiment of the invention, the acetabular insertion handlecould be hollow along the center axis to accept a drill bit. The surgeoncould impact the acetabular component into the acetabular bone and thendrill through the insertion handle and into the acetabular bone. Thedrill bit and insertion could have a mechanical stop to prevent thesurgeon from drilling too far into the patient's pelvis. This mechanicalstop could be set to allow the surgeon to drill 10 mm at first. If thesurgeon did not penetrate through the acetabular bone and into the innerpelvis, then the surgeon could set the mechanical stop at 15 mm anddrill again. These steps could be repeated until the surgeonsuccessfully and safely drilled through the acetabular bone or medialwall of the acetabulum. The drill bit could have a depth gauge on it ora separate depth gauge could be used and referenced off of the insertionhandle.

FIG. 2 depicts a frontal view of one exemplary embodiment of anacetabular anchoring device or endobutton 10, showing variouspositioning sutures 50, 60 on either end of the endobutton and atensioning suture 30 that could connect to the acetabular component (notshown). The positioning suture 50, 60 could loop through a hole 20,25 inthe endobutton and then over the edge of the endobutton. The tensioningsuture 30 could loop through one hole 40 and back through the anotherhole 45.

The endobutton could have a narrow dimension and a long dimension sothat the endobutton could be passed through a long tunnel in the boneand then flipped to gain purchase of the surface of the inner wall ofthe pelvis. The endobutton could be made from metal, polymer or anyother material commonly used in surgeon. It could be permanent orabsorbable.

The positioning sutures could loop around the ends of the endobutton andallow the surgeon to advance either one side or both sides together. Thepositioning suture could be made out of any material like nylon. Ifdesired, the positioning suture could be removed at any point during thesurgery, such as the middle of the operation, after the endobutton waspositioned on the inner wall of the pelvis.

The tension suture could be any heavy-duty suture material (or othermaterial) that could be designed and or appropriately sized to withstandconsiderable force. Exemplary materials can include Fiberwire, Mersilenetape, metal wire or other braided sutures, which are desirablynon-exclusive examples of possible material that could be used.

FIG. 3 depicts a cross sectional view of an acetabular component 70, adome screw 80, and an endobutton 10 that has been preloaded inside ofthe dome screw 80. The dome screw could have screw threads 100 or otherfeatures that could attach to the screw threads 75 of the dome screwhole of acetabular component. The acetabular dome screw hole threads 75could be the same screw threads used to accommodate the acetabularinsertion handle. The dome screw could have screw threads 90 that engagethe acetabular bone. The endobutton 10 is shown inside the hollowportion of the dome screw hole.

The dome screw could be made in multiple different lengths. The lengthof the screw needed and/or desired could be determined by the surgeonusing a depth guide to measure the thickness of the medial wallacetabular bone as described above. The surgeon might want to use a domescrew somewhat shorter than the thickness of the bone to ensure adequatecompression between the inner wall of the pelvis and the endobutton. Thedome screw could be available with different threads to attach todifferent acetabular components.

The endobutton is shown preloaded in the dome screw, but couldalternatively be packaged and inserted separately without the dome screwattached. The dome screw could then be inserted after the endobutton isflipped and secured to the inner wall of the pelvis.

FIGS. 4a and 4b depict frontal views of the positioning sutures 110attached to near end 20 and far end 25 of the endobutton 10, the tensionsutures 30 attached to the endobutton 10, a cannulated metal sleeve 120that houses the positioning suture 110, a short handle 130 that allowsthe surgeon to push and pull the near end of the endobutton through themetal sleeve and suture, a long handle 140 that allows the surgeon topush and pull the far end of the endobutton through the other metalsleeve and suture, and the positioning suture 115 exiting the handles.

The cannulated metal sleeve could act similar to a Huston suture passer.The positioning suture could pass through the handle, through the metalsleeve, through the hole in the endobutton, around the end of theendobutton, back into the metal sleeve, back through the handle and outthe end of the handle. There could initially be some mild tension of thepositioning suture to minimize the loop made at the endobutton end. Thesurgeon could push and pull on the handles to move the metal sleeve andthereby move each end of the endobutton independently. The metal sleevecould pass through the inner hollow portion of the dome screw and intothe drill hole in the acetabular bone. The handles could therefore beable to push the endobutton through the hollow portion of the domescrew, through the drill hole in the acetabular bone, and out of thepelvic bone and into the inner pelvic cavity.

The two handles of the endobutton could be designed so that the far endsof the handles could initially be flush as shown in FIG. 4a . The shorthandle could be attached to the end of the endobutton that was closestto the acetabular component. The surgeon could initially advance bothhandles to the depth measured by the depth gauge during the bonedrilling process. The measurement could correspond with the endobuttonleaving the drill hole and passing the surface of the inner wall of thepelvis. The surgeon could then advance the short handle, to desirablyadvance just the end of the endobutton that was closest to theacetabular component until the opposite end of the two handles wereflush, such as seen in FIG. 4b . The surgeon could then pull back on thetensioning suture or the positioning sutures to pull the endobuttonflush with the inner wall of the pelvis.

The surgeon could remove the positioning suture by pulling on just oneend of the positioning suture 115 as it exits the handle. The other endof the positioning suture could be pulled through the hole in theendobutton and back out of the metal sleeve. The removal of thepositioning suture could be done before the surgeon tensioned thetensioning suture so that the positioning suture could move through thehole in the endobutton easier.

FIG. 5 depicts an endobutton 10 on one side of a bone 150 (acetabulum),a tension suture 30 attached to the endobutton 10, an acetabularcomponent 70 implanted in a bone 150 (acetabulum), a dome screw 80 thatis to be inserted through the dome hole 75 in the acetabular componentand into a drill hole 155 that has been made in the acetabular bone 150.

The surgical scenario shown in FIG. 5 may be particularly useful wherethe surgeon has inserted the acetabular component, drilled the drillhole in the acetabular bone, and chose to insert the endobuttonseparately from the dome screw. Once the endobutton has been inserted,flipped, and positioned on the inner wall appropriately, the surgeoncould then insert the dome screw into the acetabular component andattach the tensioning suture to the dome screw.

FIGS. 6a and 6b depict an endobutton 10 on one side of an acetabularbone 150, a tension suture 30 attached to the endobutton, an acetabularcomponent 70 implanted on the opposite side of the acetabular bone fromthe endobutton, a dome screw 80 attached to the acetabular component viascrew threads 100, an interference screw 180 shown outside of the domescrew, and screw threads of the interference screw 170 that can engagethe inner screw threads 160 in the dome screw and secure fix the tensionsuture to the dome screw. FIG. 6b further depicts the tension sutures 30bypassing in the inner screw threads 160 and running through a smallchannel 200 in the dome screw 80. FIG. 6b further depicts an indentation190 in the screw head of the dome screw that could accept a largescrewdriver 210 like a hex head screwdriver.

The surgical scenario shown in FIGS. 6a and 6b may be particularlyuseful where the surgeon has inserted the acetabular component, drilledthrough the acetabular bone and to the inner pelvis, inserted the domescrew, and then advanced the endobutton to the inner wall of the pelvis.

A screwdriver 210 that inserts the dome screw into the acetabularcomponent could be hollow to allow it to house the positioning suture110, the metal sleeves 120, and the short 130 and long 140 handles. Thesurgeon could use this screwdriver to thread the dome screw into theacetabular component and then immediately (if desired) advance the twoends of the endobutton as described above. The tensioning suture couldrun through the center hollow opening of the screwdriver. Gentle tensioncould be placed on the tensioning suture to ensure that the endobuttonwas properly positioned and the positioning suture 110 and the metalsleeves 120 could be removed from the hollow portion of the dome screwand the screwdriver. The tensioning suture could be attached to amechanical gear inside the screwdriver. A part of the screwdriver couldbe turned or twisted to activate the gears and tighten the tensioningsuture around a rotating gear or cylinder. Many arrangements of gearingor other similar systems of gears or other devices exist in orthopedicsfor tightening of cerclage wires around bones, which may be useful inconjunction with various features of the embodiments described herein.The interference screw could be inserted through the opening in thescrewdriver and fastened to the inside of the dome screw (FIG. 7a ) todome screw and/or the interference screw could have some deformable partsuch as a small channel 200 that could be collapsed when theinterference screw is threaded into the dome screw, desirably firmlyattaching the tensioning suture to the dome screw. Alternative suturefixation methods are possible as well, including by tying the suture.

FIG. 7a depicts an endobutton 10 on one side of a bone (acetabulum), atension suture 30 attached to the endobutton and the dome screw via theinterference screw 180, an acetabular component 70 implanted in anacetabulum bone 150, a dome screw 80 attached to the acetabularcomponent, an interference screw threads 170 engaging the inner domescrew threads, the tension suture secured to the dome screw by theinterference screw before it runs through the channel in the dome screw200, and the screwdriver attached to the dome screw. FIG. 7a shows anexample of a final completed structure. In this embodiment, theinterference screw has been advanced into the dome screw to securelyattach the tension suture to the dome screw.

FIG. 7b depicts the final construct with the screwdriver removed and thetension suture cut at the face of the dome screw. Once the interferencescrew has been engaged and securely attached the tensioning suture tothe dome screw, the tensioning suture could be detached from gearmechanism of the screwdriver, the screwdriver could be removed, and thetensioning sutures could be cut (if desired).

The screwdriver 210 could take on many shapes and sizes. The purposes ofthe screwdriver could include threading the dome screw into theacetabular component, allowing passage of the metal sleeves 120 thatcould allow the endobutton to flip, measuring of the distance that thehandles 130 & 140 travel (and thus the distance that the two ends of theendobutton travel), tensioning the tensioning suture with somemechanical advantage through a gear or lever, and/or allowing theinterference screw to be inserted while the tensioning suture hadadequate tension. The screwdriver could remain attached to the domescrew through the whole deployment of the endobutton, if desired.

The screw threads in the dome screw and the screw threads in theacetabular component could engage to form a fixed angle device. Theangle between the acetabular component and the dome screw could then beheld constant and offer further fixation of the acetabular component tothe acetabular bone.

The drawings and text above refer to the implantation of an acetabularcomponent into an acetabular bone for descriptive purposes only. Similarprinciples as those described above could be applied to other jointslike the knee, ankle, feet, shoulder, elbow, back and wrist.

INCORPORATION BY REFERENCE

The entire disclosure of each of the publications, patent documents, andother references referred to herein is incorporated herein by referencein its entirety for all purposes to the same extent as if eachindividual source were individually denoted as being incorporated byreference.

EQUIVALENTS

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The foregoingembodiments are therefore to be considered in all respects illustrativerather than limiting on the invention described herein. The scope of theinvention is thus intended to include all changes that come within themeaning and range of equivalency of the descriptions provided herein.

Many of the aspects and advantages of the present invention may be moreclearly understood and appreciated by reference to the accompanyingdrawings. The accompanying drawings are incorporated herein and form apart of the specification, illustrating embodiments of the presentinvention and together with the description, disclose the principles ofthe invention.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it will be readily apparent to those of ordinary skill inthe art in light of the teachings of this invention that certain changesand modifications may be made thereto without departing from the spiritor scope of the disclosure herein.

What is claimed is:
 1. An acetabular cup system comprising: anacetabular cup having a wall with an inner surface and an outer surface,the acetabular cup including a fixation opening through the wall, thefixation opening having a threaded inner surface extending from theinner surface to the outer surface, a dome screw including a head and ashaft, the head of the dome screw including a threaded outer portion forengaging with the threaded inner surface of the fixation opening, thedome screw including a screw lumen extending longitudinally through thehead and shaft, an elongated button having at least one button opening,the elongated button being sized to at least partially fit within thescrew lumen, and a flexible structure extending between the elongatedbutton and the dome screw, the flexible structure including a buttonalignment indicator, the flexible structure attached to the dome screwby an adjustable fastener, wherein the flexible structure can beconnected to the dome screw at a plurality of locations along theflexible structure.
 2. The acetabular cup system of claim 1, wherein thehead of the dome screw includes an outer diameter that is larger than anouter diameter of the shaft.
 3. The acetabular cup system of claim 1,wherein the shaft includes a first longitudinal length, and the headincludes a second longitudinal length, and the first longitudinal lengthis greater than the second longitudinal length.
 4. The acetabular cupsystem of claim 1, wherein the fixation opening has a bore depth, and alongitudinal length of the dome screw is greater than the bore depth. 5.The acetabular cup system of claim 1, wherein the a flexible structureextending between the elongated button and the dome screw comprises afirst suture, a second suture and a third suture, the first sutureattached to a first button opening adjacent to a first end of theelongated button, the second suture attached to a second button openingadjacent to a second end of the elongated button, and the third sutureattached to at least one opening positioned between the first and secondopenings.
 6. The acetabular cup system of claim 5, wherein the firstsuture includes the button alignment indicator.
 7. The acetabular cupsystem of claim 1, wherein the dome screw further comprises a lockingmechanism for securing the flexible structure to the dome screw.